It has long been a common practice in the well art to suspend an inner pipe, typically a casing string, concentrically within an outer member, typically an outer casing string or a wellhead member, by means of a hanger comprising a hanger member connected to the inner pipe and having a downwardly directed shoulder which engages an upwardly directed shoulder on the outer member as the inner pipe is run in. As the art developed, it became necessary to minimize the annular space between the inner and outer hanger members and prior art workers have developed hangers employing a retractable hanger device carried by a mandrel on the inner pipe and capable of expanding into engagement with an outer hanger member when, as the inner pipe is run in, the mandrel reaches the outer hanger member. Pipe hangers of this type have become particularly important with the advent of offshore practices in which the hanger is located at the mudline and the outer pipe above the wellhead is of the same diameter as the outer casing below the wellhead and the annular space available for the hanger is relatively small. Such hangers sometimes employ an annular retractable hanger means in the form of a circular series of mutually independent segments with each segment being spring-biased outwardly as shown, for example, in U.S. Pat. No. 3,472,530 Fowler. In other prior-art devices of this type, the retractable hanger device is in the form of a split ring as seen, for example, in the following U.S. patents:
U.S. Pat. No. 3,420,308; Putch
U.S. Pat. No. 3,741,589; Herd et al.
U.S. Pat. No. 3,800,869; Herd et al.
U.S. Pat. No. 3,971,576; Herd et al.
U.S. Pat. No. 3,974,875; Herd et al.
Though hangers of this general type have achieved considerable success, they still present problems which increase in severity as the annular space available at the hanger decreases and the weight of the pipe string to be suspended increases. It has proved difficult to design either an assembly of segments or an integral split ring which is dimensioned to be accommodated in the small annular space available adequately strong to carry the heavy loads applied by the suspending pipe and, while adequately resiliently compressible to successfully enter the outer body from which the pipe is to be suspended, is yet effective to come automatically into full positive engagement with the outer body as landing of the string is completed. Further, hangers of this type require that the retractable hanger device, whether it be made up of a plurality of segments or be in the form of a split ring, be initially secured in releasable fashion to the mandrel in such fashion that, once the retractable hanger device has engaged the outer body, further downward movement of the mandrel is possible to complete the operation. In some cases, the segments or the ring have been releasably secured to the mandrel by shear members, but this has the disadvantage that care must be taken to avoid portions of the shear member dropping into the annulus to become damaging debris. While other releasable retaining devices have been proposed, there has been a continuing need for a simple and more dependable device.